Mathematical modeling of combinatorial regulation suggests that apparent positive regulation of targets by miRNA could be an artifact resulting from competition for mRNA

(A) Scaled protein steady-state level for single mRNA–single miRNA as a function of rate of formation of miRNA1 (b₁^μ molecules/sec), translation by complex c₁₁ (b₁₁^p/sec), and formation of complex c₁₁ (k₁₁⁺/molecule/sec). Position marked with × corresponds to reference values of b₁^μ, b₁₁^p, and k₁₁⁺ as listed in Table 2. Other parameter values constant, given in Table 2. (B) Line plot of scaled protein level for one miRNA, interacting with single mRNA. Lines represents specific parts of A, for constant complex formation rate (k₁₁⁺=0.2943/molecule/sec). For all constant levels of b₁₁^p, increase in rate of miRNA formation (b₁^μ) leads to decrease in protein ratio levels. Reference values of b₁^μ, b₁₁^p, and k₁₁⁺ listed in Table 2 are 1 molecule/sec, 0.001/sec, and 1/molecule/sec. Other parameter values are constant, given in Table 2.